pragma once and for all

Fix licenses

sel4utils: Align stack pointer for new threads

sel4utils: Trivial whitespace

sel4utils: Add type for thread entry point

Our thread-starting code assumes that its entry point is a function.
Previously, a void pointer was used as the type of the entry point.
Now thread entry points must be pointers to functions with a signature
void (*)(void*, void*, void*).

libsel4utils: Move src/helpers.h to global include

The utility functions in this header are useful outside of just libsel4utils